3.
如图所示,下列判断中错误的是( )
| A. | 因为AD∥BC,所以∠3=∠4 | B. | 因为AB∥CD,所以∠ABC+∠C=180° | ||
| C. | 因为∠1=∠2,所以AD∥BC | D. | 因为∠A+∠ADC=180°,所以AB∥CD |
20.
如图,若△ABC的周长为20,则AB的长可能为( )
| A. | 8 | B. | 10 | C. | 12 | D. | 14 |
17.
将一个长为10cm、宽为8cm的矩形纸片对折两次后,沿所得矩形两邻边中点的膀(如图①)剪下,将剪下的图形打开,得到的菱形ABCD(如图②)的面积为( )
0 294412 294420 294426 294430 294436 294438 294442 294448 294450 294456 294462 294466 294468 294472 294478 294480 294486 294490 294492 294496 294498 294502 294504 294506 294507 294508 294510 294511 294512 294514 294516 294520 294522 294526 294528 294532 294538 294540 294546 294550 294552 294556 294562 294568 294570 294576 294580 294582 294588 294592 294598 294606 366461
| A. | 10 cm2 | B. | 20 cm2 | C. | 40 cm2 | D. | 80 cm2 |